Method of producing cotton cordage



Patented Sept. 14, 1948 METHOD OF PRODUCING COTTON CORDAGE Charles F. Goldthwalt and Herbert 0. Smith, New Orleans, La., asslgnors to the United States of America as represented by the Secretary of Agriculture N0 Drawing. Application July 10, 1945, Serial No. 604,288

3 Claims. (Cl. 57-164) (Granted under the act of March 3, 1883, as

This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to us of any royalty thereon.

This invention relates to cotton cord, and in particular to a method of producing the cord in such manner as to enhance its tensile strength and its resistance to flexure-fatigue when used under conditions subjecting it to relatively high temperatures for long periods of time, such as encountered by reinforcing cords for pneumatic tires. power belts, and so forth.

It is conventional in commercial processes to treat cotton yarn used for cords with a strong alkali such as sodium hydroxide, wash out and neutralize residual alkali with an acid, wash with water the yarn thus treated, and dry it, all with great care to avoid any shrinkage of the yarn, this in general being the process known as mercerization.

Cord made from yarn processed in this manner has a somewhat increased resistance to heat, that is, under condition of extended high temperatures, such cord will maintain its tensile strength and resistance to flexure-fatigue better than if not treated at all. We have found, however, that with this process the cord is not as resistant to heat as cord produced from yarn treated in a manner allowing considerable longitudinal shrinkage thus to allow maximum swelling of the cotton and in which residual alkali is removed by means not requiring neutralization with an acid.

In general, according to the present invention, cotton yarn is treated. with an alkali hydroxide, preferably sodium hydroxide, inthe manner of mercerization, usinga concentration. of the alkali of about 20 percent to 25 percent by weight, but incontrast tothe usual mercerization process. the

cotton is giigen;specialopportunity to swell which is, manifested; lay-longitudinal, especially high ,sshrinkageof-the yarn, such as 15 percent. The ,sacidifica-tion orsouring; step is also omitted. and the residual alkali is washed out with a non-acid --medium, either water alone or, in preference to this, the lasttracesof the alkali are neutralized with an aqueous solution of a salt, such as sowashed outmore readily thanthe residualalkali without leaving any traces of chemicals or cotamended April 30, 1928; 370 O. G. 757) ton impurities which are acid. The salt used, although slightly alkaline in solution, reacts with the residual alkali like an acid, forming in the case of sodium bicarbonate normal sodium carbonate.

The yarn is then dried and twisted into cord in the regular manner, thus regaining most of the original length by tension applied during the twisting.

We have found that it is preferable to employ yarn at a minimum practical spinning twist, that is, with a minimum of restraint due to yarn twist, so as to allow as full effect of the alkali swelling of the cotton as is possible. In order further to promote this swelling, the yarn is treated in the alkali hydroxide without any tension whatever being applied to the yarn except for a small amount due to its own weight and that necessary to give a minimum of pull required to move the yarn in the apparatus during the treatment with the alkali hydroxide. Applying tension while the yarn is in the alkali decreases the amount of swelling of the cotton, thus decreasing the heat resistance. To insure a maximum of resistance to heat, the alkali hydroxide treatment is operated under conditions which are not merely at low tension or at no tension, but are practically the opposite of tension in the ordinary sense. Freedom to that is, a tension built up by the cotton swelling against the yarn twist and acting in the direction opposite to that usually applied, is allowed. During washing, partial recovery from shrinkage (about 4 percent or 5 percent) may take place due probably to deswelling and to straghtening of slight kinks formed during the shrinking. This is limitedto an amount, however, that doe not represent forcible stretching or mechanical deswelling of fibers which are swollen by the alkali hydroxide.

The advantage of this allowance of longitudinal shrinkage thus to allow maximum swelling of the cotton is believed to be explained by attributing the improved heat resistance to as complete conversion as possible of the native cotton cellulose to the mercerized type of cellulose, The improved flex life is attributed to the most complete possible disorientation and reduction of crystallinity, including an increase in the amount of amorphous cellulose at the expense of the crystal form, produced by the free and complete swelling of the cotton fibers. This explanation is supported by the comparative X-ray diffraction diagrams made from cottons processed under different conditions of swelling, or longitudian acid, This we attribute to the theory that minute quantities of the acid are entrapped by the cellulose structure of the cotton and are not removed by the subsequent washing, and that these minute quantities react with the cellulose under conditions of exposure to the high temperatures for long periods of time, and thereby weaken the cord in tensile strength and fiexurefatigue resisting qualities more than when the cotton is not treated with a neutralizing acid. It also appears that, independently of the eiTect of the traces of retained strong acid, other acids are formed from the natural impurities of the cotton due to the strong acid treatment. These other acids cannot be washed out, and they cause profound degradation of cellulose during long periods of heating at high temperatures.

The advantages of the improved process as explained above are illustrated by the data set out in the. following tables.

Table I illustrates the increased tensile strength obtained under conditions of heating. due to the especially high shrinking feature of the process.

' The tests were made on similar size yarns, the

first item being untreated yarn. the second yarn mercerized according to the commercial process, and the third yarn produced by allowing percent shrinkage as in the present process, but with acid neutralization of residual alkali. The tensile strengths of the yarns were determined for each item, first, by breaking the yarn in standard atmospheric conditions (standard atmcsp eric condi ions being at 65 percent relative humidity. and 70 F.). and second, by breaking the yarns while still not after heating for 5 minutes at 266 F. The percentage strength retained is determined by dividing the tensile strength obtained under the heating conditions by that obtained under the standard atmospheric conditions.

Table I Percentage tensile strength retained Kind of cottonyarn aiter heating for 5 minutes at 266 F.

Untreated 48 Commercial memorized 72 1 shrinkage as in the present procesabut with acid neutralization of residual alkali.. 87

The above table shows that, even under the very mild conditions or heating for 5 minutes at 266 F., there is a considerable increase in strength retention oi. the yarns processed by especially high shrinking according to the present inventicn, even witnemployment of an acid neutralization step. overthe strength retention of yams memorized bythe commercial process.

Table II is similar to Table I except that the tests were made on cords twisted from the yarns.

Table II Percentage tensile strength retained Kind of cotton yarn after heating for 5 minutes at 266 Untreated 52 Commercial mercerized 75 15% shrinkage as in the present process, but

with acid neutralization oi residual alkali. 82

Table III illustrates the increase in tensile strength retained by cords made according to the present process as compared to cords made from untreated cotton yarn under more drastic conditions of longer periods of heating and higher temperatures. Items 1 and 2 represent cords made from ordinary untreated cotton yarn, and item 3 cords made according to the present process using both the especially high shrinking feature and without acid neutralization of residual alkali. The breaking tests were made in this instance on dry cord rather than on cords under standard atmospheric conditions.

Table III Percentage tensile strength retained Alter heating at 265 After heating for 5 hours Kind of cotton 1 cord 384 576 768 7 hours hours hours 302 F. 347s F. 392 F.

Untreated cotton Item 1 62 49 41 93 86 28 Untreated .cotton Item 2 51 46 37 87 31 Made according to a present process Item3 70 58 52 100 100 Table IV illustrates, the increased tensile strength retained due to the omission of the acid neutralization of the residual alkali. The table shows two experiments in each of which a mercerized cotton yarn (mercerized without especially high shrinking) wasneutralized with an acid treatment followed by thorough washing with water while an identical sample was washed thoroughly to free it from residual alkali without any neutralizing agent being used.

Table IV Percentage i I strength re- Experiment Kind oi cotton yarn 23? 52 v hoursat329 1 Mercerized, with acid treatment"..- 48. 6 Mercerized, without acid treatment. 72.8 3 Mercerized, with-acid treatment 39. 6 Mercer zed, without acid treatment. 68. 7

, The eflect of the omission of the acid treatment shown in the above table is quite pronounced. Even better results are obtained it the alkali hydroxide be neutralized with a mild salt, such as sodium bicarbonate, and the yarn then washed.

This is illustrated in Table V, in which cotton yarns were tested, the first having been mercerized using a sulfuric acid neutralizing treatment, the second mercerized without the acid treatment and thoroughly washed with water, and the third mercerized using a sodium bicarbonate solution treatment to neutralize the residual alkali and then washed with water.

The foregoing five tables all show the increased tensile strength retained due to the especially high shrinking and the non acid washing features of the invention used either separately or together. More pronounced, however, is the increased resistance to flexure-fatigue at elevated temperature, as is illustrated in.Table VI. In this table, the data are based on two experiments in each of which various types of cotton cords were subjected to fiexure under similar conditions at 248 F., and the number of flexures before breaking recorded, experiment 2 differing Having thus described the invention, what is claimed is:

1. A method of producing cotton reinforcing cord for pneumatic tires, power belts, and so forth, comprising forming ordinary cotton into a yarn or minimum practical spinning: twist,

treating the yarn with an alkali hydroxide in a concentration of about 20 percent to 25 percent by weight while allowing the yarn thus treated from experiment 1 in that the cord used had been given an extra stretching treatment to make it stronger before the flexure tests were made. All cords in each experiment were carefully made so as to give results strictly comparative.

Table VI Number of fiexures at 248 F. before breakage Kind of cotton cord Experi- Experiment 1 ment 2 Untreated 3, 006 Commercially meroerized 3, 143 Especially high shrinking as in present process, but with acid treatment..... 5, 159 7, 284 Present process, especially high shrinking and without acid treatment- 8, 124 9, 672

to shrink about 15 percent of its original length to allow maximum swelling of the cotton, washing out residual alkali with a non-acid aqueous medium, drying the yarn, and twisting the dried yarn into cord, thus regaining most of the original length by tension applied during the twisting.

2. The method of claim 1, in which the nonacid aqueous medium is water.

3. The method of claim 1. in which the nonacid aqueous medium is a water solution of a salt which neutralizes the residual alkali.

CHARLES F. GOLDTHWAIT. HERBERT 0. SMITH.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 2,153,963 Lejenne et al. Apr. 11, 1939 2,254,740 Hansen et al. Sept. :2, 1941 FOREIGN PATENTS Number Country Date 517,751 Great Britain Feb. 7, 1940 OTHER REFERENCES Mercerising, by J. T. Marsh, published; by D. Van Nostrand and 00., New York, N. Y., 1942. 

